1. Our goal is to clone genes coding for lymphocyte cell surface differentiation antigens in the mouse Ly-6 cluster using DNA mediated gene transfer, fluorescence activated cell sorting and cDNA subtraction. There are at least eight mouse lymphocyte antigens whose tissue distribution is unique but whose genes all map to the same region of chromosome 2. By cloning genes for these antigens, we will determine whether there is a family of tightly linked genes or whether there is one or a few genes which are expressed differently during differentiation. In addition, with the cloned genes we can study how their expression is regulated during differentiation and what the functions of these antigens may be. 2. To use the genes coding for mouse antigens in the Ly-6 cluster for screening human DNA libraries to identify homologous sequences and discover whether a similar gene cluster occurs in humans. 3. To make chromosome assignments for genes coding for human lymphocyte differentiation antigens using a new approach with somatic cell genetic techniques. 4. To establish a panel of mouse L cell transfectants where each transfectant expresses a different human leukocyte differentiation antigen. This panel will be used for characterizing and comparing monoclonal antibodies submitted to the Third International Workshop and Conference on Human Leukocyte Differentiation Antigens.